def f(n):
    for i in range(2, n):
        if n % i == 0:  return False
    return True


cif = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"]
left = []
right = []
s = input()
a = s.split()
b = ""
for x in a:
    b += str(cif.index(x))
b = int(b)
for c in range(b, 1015):
    if f(c):
        right.append(c)
for c in range(2, b):
    if f(c):
        left.append(c)

if b - max(left) <= b - min(right):
    print(max(left))
else:
    print(min(right))
